1. Field of the Invention
This invention relates to a gas compressor control device and a gas turbine plant control mechanism, which are designed to be capable of suppressing a rise in the pressure of a fuel gas supplied to a gas turbine, even if load rejection or load loss occurs.
2. Description of the Related Art
In a gas turbine plant, as shown in FIG. 4, a gas turbine 2 for rotationally driving a generator 1 is supplied with a fuel gas from a gas compressor 4 via fuel gas piping 3. That is, the fuel gas for use in the gas turbine 2 is pressurized by the gas compressor 4 to a pressure suitable for the gas turbine 2.
The amount of fuel consumed by the gas turbine 2 varies with a generator load required of the gas turbine 2. In detail, when a gas turbine generator output increases, a fuel gas pressure P2 at the inlet of the gas turbine lowers, so that the gas compressor 4 is further required to raise the pressure of the fuel gas. When the gas turbine generator output decreases, on the other hand, the fuel gas pressure P2 at the gas turbine inlet increases, so that the gas compressor 4 is required to lower the pressure of the fuel gas.
A conventional concrete control method for controlling the gas turbine 2 and the gas compressor 4 will be described hereinafter.
As shown in FIG. 4, a pressure control valve 5 and a flow control valve 6 are interposed in the fuel gas piping 3. The pressure control valve 5 is disposed upstream (closer to the gas compressor 4), while the flow control valve 6 is disposed downstream (closer to the gas turbine 2).
A gas turbine control device 10 controls the valve opening of the flow control valve 6 (i.e. PID control) such that a deviation between an actual generator output W1 and a preset target generator load set value W0 is zero. The gas turbine control device 10 also controls the valve opening of the pressure control valve 5 (i.e. PID control) such that a deviation between a flow control valve differential pressure ΔP1, which is the difference between the fuel gas pressure upstream from the flow control valve 6 and the fuel gas pressure downstream from the flow control valve 6, and a preset flow control valve differential pressure set value ΔP0 is zero.
The gas compressor 4, on the other hand, is provided with a recycle pipe 7 for returning the fuel gas from the gas compressor outlet to the gas compressor inlet, a recycle valve 8 interposed in the recycle pipe 7, and an IGV (inlet guide vane) 9 for controlling the amount of air taken into the gas compressor 4.
A gas compressor control device 20 finds P0-P1, which is a deviation between a fuel gas pressure P1 at the gas compressor outlet and a preset fuel gas supply pressure set value P0. Using a control function FX1 for the recycle valve 8, the gas compressor control device 20 controls (PID control) the valve opening of the recycle valve 8 according to the deviation P0-P1. Using a control function FX2 for the IGV 9, moreover, the gas compressor control device 20 controls (PID control) the valve opening of the IGV 9 according to the deviation P0-P1.
Namely, the gas compressor control device 20 exercises control to operate the IGV 9 and the recycle valve 8 of the gas compressor 4 so that the fuel gas pressure P1 at the gas compressor outlet is constant. Concretely, the gas compressor control device 20 controls the openings in such a manner as to decrease the opening of the recycle valve 8 and increase the opening of the IGV 9 when exercising control for raising the fuel gas pressure P1, and to increase the opening of the recycle valve 8 and decrease the opening of the IGV 9 when exercising control for lowering the fuel gas pressure P1.
Generally, the gas turbine 2 and the gas compressor 4 are produced by different manufacturers, and it has been common practice that the gas turbine 2 and the gas compressor 4 are not cooperatively controlled.
In gas turbine power generation equipment having a gas turbine and a generator connected together, there has been a technique for exercising preceding control in order to prevent misfire or back fire of a combustor due to combustion instability (see, for example, Japanese Unexamined Patent Publication No. 1994-241062).
If the load on the gas turbine 2 falls abruptly, namely, if load rejection (main shut-off device open) occurs or load loss of the gas turbine occurs, the fuel gas pressure P2 (P1) at the gas turbine inlet (the gas compressor outlet) sharply increases. In this case, conventional simple one-loop feedback control over the pressure on the gas compressor 4, as shown in FIG. 4, is not enough to deal with this sharp increase. Thus, the fuel gas pressure P2 (P1) markedly rises, and then lowers to the desired pressure.
As a result, differential pressure control of the gas turbine may fail to accommodate such pressure changes, so that an excessive amount of fuel is charged into the gas turbine 2, causing breakage to the combustor or fuel oscillations.
Conventionally, therefore, a great distance has been provided between the gas turbine 2 and the gas compressor 4 to lengthen the fuel gas piping 3 and ensure a sufficiently large piping volume, thereby absorbing the elevation of the fuel gas pressure due to a sudden load fall (load rejection, load loss) of the gas turbine.
Recently, however, it has been required to construct a power plant in a small premises area in pursuit of economy. With this restricted premises area, the conventional method of securing long piping between the gas turbine and the gas compressor is nearing its limits.